1. Field of the invention
The present invention relates to a hard capsule for pharmaceutical drugs, specifically a hard capsule of a lower water content and with no use of known gelatin as the base material. More specifically, it relates to a hard capsule for pharmaceutical drugs using a water-soluble cellulose derivative as the base, and a method for producing the same.
2. Prior Art
As has been known, hard capsules for pharmaceutical drugs are molded from film compositions, wherein gelatin is generally used as the base material to which are added a plasticizer such as glycerin and sorbitol, and optionally, an opaquer, a dye or pigment. Such capsules generally contain about 10 to 15% by weight of water in the capsule film thereof.
If the water content in the capsule film decreases to be less than 10% by weight, the plasticity of the film is lost, resulting in the distinctive deterioration of the impact resistance during the filling process of drugs into the capsules with the outcome of no endurability of the use thereof. Irrespective of emptiness or fillingness of drugs, the film shrinks when the water content in the film is decreased during the storage of the capsules, inevitably involving the loosening of the engagement of the caps with the capsule bodies over time. Therefore, it is essential that such known gelatin hard capsules should contain a given amount of water as has been described above.
However, such gelatin hard capsules may induce disadvantages including the reduction of the titers, deterioration and color change of drugs filled therein and the insolubility of the capsule film, because the drugs are decomposed by the water contained in the capsule film if the drugs filled therein are readily hydrolyzed or two or more drugs with interactive activity to each other are contained therein.
In order to overcome these drawbacks, there have been made a variety of improvement and propositions over hard capsules for pharmaceutical drugs. For example, Japanese Patent Publication No. 47- 4310 discloses a method for producing a hard capsule comprising using as a base material a water- soluble cellulose ether which is produced by substituting a part or all of the hydroxyl groups of cellulose with an alkyl group or a hydroxyalkyl group, immersing a molding pin in the water-soluble cellulose ether solution, thereby forming a capsule film. Japanese Patent Laid-Open Nos. 61-100519 and 62-266060 disclose a method for producing a hard capsule, comprising compounding the above-said water-soluble cellulose ether with polyvinyl alcohol (PVA), and yielding a hard capsule from such water-soluble immersing solution.
However, these capsules for pharmaceutical drugs are produced by immersing a molding pin in an immersing solution of the water-soluble cellulose derivative as the base material, heating just the molding pin or the film attached to the pin thereby effecting gelation prior to molding, so that the immersing solution of the base material is never gelatinized but the solution is then fallen down from the molding pin if heating is not done sufficiently. Thus, capsule films practically cannot be obtained. If the heating temperature is too high, disadvantages such as wrinkle induction into the films may be caused during gelation. In the latter case, a slight amount of the gel is solubilized into water when the water-soluble cellulose derivative attached to the molding is immersed in water pin at a higher temperature for gelation. Therefore, it is difficult to obtain a uniform film, and such film may frequently develop cracking during the detachment of the molded article, i.e. the capsule film after drying, from the molding pin, due to the lower jelly strength thereof. In any case, it is difficult to obtain a hard capsule for pharmaceutical drugs with a lower water content in practical sense. Further, specified apparatus and procedures are required for practicing these capsule production methods, so that the most commonly known capsule manufacturing apparatus for immersion and molding of the conventional gelatin capsules cannot be used as it is.